1. Field of the Invention
The present invention relates to an image forming device, i.e., an office machine such as a laser printer or a copy machine, and more particularly, to an apparatus to switch a paper feed direction of an office machine capable of reducing a resistance against a paper while feeding the paper to prevent the paper from being blocked due to jamming or curling.
2. Description of the Related Art
Generally, an image forming apparatus for duplex (double-sided) printing, for example, a duplex printing laser printer 1 shown in FIG. 1 includes a paper feeding cassette 10 to stack papers, a pickup roller 20 disposed at an upper portion of the feeding cassette 10 to pick up a paper P, a paper feeding guide 22 forming a paper feeding path A to guide the paper P picked up by the pickup roller 20, and a developing unit 30 to form a toner image on a side of the paper P fed through the paper feeding guide 22. The laser printer 1 also includes a fixing unit 40, 41 to fix the toner image formed on the side of the paper P which has passed through the developing unit 30, a feeding roller 50 to feed the paper P which has passed through the fixing unit 40, 41, and a paper discharging roller 60 disposed at an upper side of the feeding roller 50 to discharge the paper P. The laser printer 1 further includes a paper duplex guide 62 forming a paper re-feed path B to re-feed the paper P discharged through the paper discharging roller 60 in order to print the other side of the paper P in a duplex printing mode, and first and second duplex rollers 70, 90 to re-feed the paper P through the paper duplex guide 62.
The developing unit 30 includes a photoconductive drum 32 to form an electrostatic latent image by receiving a light signal such as a laser beam from an LSU (Laser Scanning Unit) 36 and a developing roller (not shown) to develop a toner image by attaching toner onto the electrostatic latent image formed on the photoconductive drum 32.
The photoconductive drum 32 of the developing unit 30 is provided at a lower portion with a transfer roller 34 to transfer the toner image formed on the photoconductive drum 32 onto the paper P.
The fixing unit 40, 41 has a fixing roller 40 and a heating roller 41 to fix the toner image transferred onto the paper P by applying heat and pressure.
A paper feed direction switching apparatus 42 is disposed in the vicinity of the paper discharging roller 60 to be elastically hinged between the paper feeding guide 22 and the paper duplex guide 62 to guide the paper P to the paper duplex guide 62 in the duplex printing mode.
As shown in FIGS. 2 and 3, the paper feed direction switching apparatus 42 includes a long shaft 44, a plurality of paper guide ribs 43 disposed at the shaft 44 at predetermined intervals across a paper feed direction to guide the paper P, an elastic spring 45 with one end 45a supported by a frame 47 (see FIG. 3) and another end 45b supported by a supporting hole 48a of a spring supporting part 48 formed at the shaft 44 to elastically restore the paper guide ribs 43 to an original position after the paper P passes through the paper guide ribs 43 while pushing the paper guide ribs 43, and a lever 46 disposed at one end 44a of the shaft 44 to remove a jammed paper P.
In order to sense that the paper P has passed, a sensor actuator 49 is disposed at another end 44b of the shaft 44 to move in association with the shaft 44 rotating when the paper guide ribs 43 fixed to the shaft 44 are pushed by the paper P. Also, a paper sensor 49a is disposed at a corresponding portion of the frame 47. The paper sensor 49a may be an optical sensor, and has a light emitting part and a light receiving part.
A duplex printing process of the laser printer 1 with the above construction will be described hereinafter. First, one of the papers P stacked at the paper feeding cassette 10 is picked up by the pickup roller 20 and then moved to the developing unit 30 through the paper feeding guide 22.
An electrostatic latent image is formed on the photoconductive drum 32 of the developing unit 30 by a laser beam emitted from the LSU 36. The laser beam corresponds to an image signal, and a toner is attached to the electrostatic latent image formed on the photoconductive drum 32 by the developing roller to be developed to a toner image which can be seen.
The toner image formed on the photoconductive drum 32 is transferred on to one side, for example, a top side of the paper P by the transfer roller 34 when the paper P is fed to the developing unit 30 through the paper feeding guide 22. The toner image transferred to the top side of the paper P is fixed thereon by the heating roller 41 and the fixing roller 40 included in the fixing unit.
The paper P which has passed through the heating roller 41 and the fixing roller 40 is fed to the paper discharging roller 60 by the feeding roller 50.
At this point, the paper P pushes the paper guide ribs 43 of the paper feed direction switching apparatus 42 from a position illustrated with a solid line to a position illustrated with a dotted line in FIGS. 1 and 3 by a rotational power of the feeding roller 50, while passing through the paper guide ribs 43. Thereafter, the sensor actuator 49 is separated from the paper sensor 49a and the paper sensor 49a senses that the paper P has passed.
In a simplex (single-sided) printing mode, the paper P is discharged to a paper tray 59 through the discharging roller 60.
However, in the duplex printing mode, the discharging roller 60 is driven to rotate backward by a separate forward/backward rotation driving controller (not shown) in correspondence with a signal generated at the paper sensor after a rear edge of the paper P is passed through the paper guide ribs 43. Thereafter, the paper P is fed to the paper duplex guide 62 without being discharged to the outside. At this point, since the paper guide ribs 43 are restored elastically to the position illustrated with the solid line in FIGS. 1 and 3, the paper P may be easily fed to the paper duplex guide 62 by the paper guide ribs 43.
The paper, which has reached the paper duplex guide 62, is fed to an arranging roller 80 by the first duplex roller 70. The arranging roller 80 is disposed to be sloped at an angle of about 5 degrees so that a leading edge of the paper P is pushed and arranged by the arranging roller 80.
The paper P arranged by the arranging roller 80 is passed through the second duplex roller 90 back to the paper feeding guide 22, and another side, that is, a bottom side of the paper P is printed on as described before, whereby the paper P is discharged to the paper tray 59.
According to the conventional laser printer 1, since the paper guide ribs 43, which guide the paper P printed on the one side thereof to a paper duplex path B, block a paper feeding path A by the elastic spring 45, the paper P encounters great resistance from an elastic force of the elastic spring 45, a weight of the paper guide ribs 43, etc., when the paper P passes through the paper feeding path A.
When the paper P encounters resistance, the paper P cannot move smoothly but is blocked due to curling and jamming, thereby degrading reliability of the printing.